Cathode-ray tube



Dec. 31, 1957 E. GUNDERT CATHODE-RAY TUBE Filed Nov. 29, 1954 F/E. l

INVENTOR. EBY/Mfd/ Gun ae r1,

United States Patent CATHODE-RAY TUBE Eberhard Gundert, Ulm (Danube), Germany, assignor to Telefuuken Gesellschaft fuer drahtlose Telegraphie m. b. H., Hannover, Germany Application November 29, 1954, Serial No. 471,787 5 Claims. (Cl. 31382) The present invention relates to a new and improved electron ray tube. More particularly, the present invention relates to a new and improved electrode structure for cathode ray tubes used in television receivers. I

To obtain electrostatic focusing in cathode ray tubes it is possible to use a unit lens or an accelerating lens. If such a lens is used and the voltage applied to the anode of the cathode ray tube is over kilovolts, it is possible to apply a comparatively low voltage to the focusing lens electrode. For example, a voltage in the region between 100 volts and 500 volts can be used for the lens electrode. Therefore, a voltage can be applied to the lens electrode which is already available in the television receiver power supply.

However, it is also necessary that the lens electrode be so dimensioned that an optimum beam diameter is obtained. The meaning of the term optimum beam diameter will be explained hereinbelow with reference to Fig. 1.

The use of a unit lens for electrostatic focusing in cathode ray tubes presents several disadvantages. Because of the high voltage applied to the anode, the high voltage insulation used in the cathode ray tube must be of the highest quality. Another disadvantage lies in the critical tolerance required for the distance between the anode parts. Also, the conventional unit lens that has been used in the cathode ray tube have been of such lengths that very high voltages are necessary to obtain the optimum beam diameter. On the other hand, by using the new and improved construction of the present invention it is possible to obtain an electrostatic focusing unit lens which provides an optimum beam diameter and yet is dimensioned so that it requires a low voltage already available in the apparatus associated with the cathode ray tube.

Accordingly, it is an object of the present invention to provide a new and improved cathode ray tube using electrostatic focusing.

Another object of the present invention is to provide a new and improved unit lens for use in cathode ray tubes.

A further object of the present invention is to provide an electrostatic focusing lens electrode adapted to be positioned in the neck portion of the cathode ray tube between the emitting surface of the cathode and the anode and wherein the distance between the emitting surface of the cathode and the anode is smaller than the diameter of the lens electrode.

With the above objects in view, the present invention mainly consists of apparatus for use in a cathode ray tube and includes a plurality of electrodes mounted within the neck portion of the cathode ray tube and including a cathode having an emitting surface, a control electrode and an anode having an entrance edge for the cathode ray beam, and a lens electrode mounted in the neck portion of the cathode ray tube between the control electrode and the anode, the lens electrode being dimensioned so that the distance from the emitting surface of the cathode to lCC - 2- the entrance edge of the anode is smaller than the diameter of the lens electrode at the entrance edge of the anode.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is a graphical representation showing the relationship between the diameter of the cathode ray beam in the-deflection plane and the diameter of the light spot at the screen of the cathode ray tube;

Fig. 2 is a longitudinal cross sectional view of the neck portion of a cathode ray tube showing one embodiment of apparatus capable of carrying out the method of the present invention.

Referring now to Fig. 1, D represents the diameter of the cathode ray beam in the deflection plane and d represents the diameter of the light spot at the screen of the cathode ray tube; The curve I is for an undefiected beam and it can be seen that the light spot diameter decreases with increase in the diameter of the deflected beam in hyperbolic fashion. The curve II is for a deflected beam and it can be seen that the light spot diameter increases substantially linearly with the increase in the diameter of the cathode ray beam.

In the usual applications of cathode ray tubes it is apparent that the displayed area on the screen of the cathode ray tube is made up of both deflected and undeflected beams. Therefore, to determine what the optimum diameter of the cathode ray beam should be in the deflection plane, it is necessary to add the two curves I and II together as shown by curve III. From this latter curve it is apparent that the optimum beam diameter is that diameter which will provide the minimum light spot diameter. This is indicated at the point 21 on the curve III.

Referring now to Fig. 2, it is seen that within the neck portion 1 of the cathode ray tube there is mounted a cathode 22, having an emitting surface 2; a control electrode 3 for controlling the brightness of the cathode ray beam on the screen of the tube; a screen grid 4; and an anode electrode 6.

Mounted between the anode electrode 6 is an electrostatic lens 5 in tubular form attached to the inner surface of the neck portion 1. The anode 6 is mounted in insulated fashion on the lens 5 by means of an insulated disk 7 so that a funnel-shaped portion 8 of the anode 6 is inserted within the lens electrode 5.

In such an arrangement I have found that over 10 kilovolts can be applied to the anode 6 while only a few hundred volts need be applied to the focusing lens 5 to obtain sharp focusing on the screen of the cathode ray tube.

To obtain the above indicated focusing results, it is advantageous to dimension the focusing lens electrode 5 in a particularmanner. In Figure 2 it can be seen that the distance a from the emissive surface 22 of the cathode 2 to the beam entrance edge 23 of the anode portion 8 is smaller than the diameter b of the lens electrode 5 at the beam entrance edge 23 that is the ratio azb is less than 1. In this manner it is possible to obtain the optimum beam diameter without requiring high voltage for the focusing lens electrode 5. Such a dimensional relationship between the cooperating parts also permits the focusing lens electrode 5 to be made of a small enough diameter to fit easily within the neck portion of the cathode ray tube.

It is of course possible to improve the actual configuration of the electrodes illustrated in Figure 2. For example the insulating disk member 7 can be formed with projecting portions to increase the leakage path thereacross. Instead of forming the anode electrode 6 with a funnel-shaped portion 8 it is possible to coat the insulator 7 which may be formed of a ceramic material with an electrically conductive coating on the side facing the focusing lens electrode 5.

It is also advantageous to magnetically shield the space in which the electrostatic field of the lens is formed. This is preferable so that the stray flux of the deflecting fields will not prematurely deflect the electron beam. Making the electrode of ferromagnetic material will accomplish this. It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of electron ray tubes differing from the types described above.

While the invention has been illustrated and described as embodied in an improved construction for a cathode ray tube, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. ln a cathode ray tube having a neck portion in combination, a plurality of electrodes mounted within the neck portion and including a cathode having an emitting surface, an anode electrode having an entrance edge for the cathode ray beam, and a control electrode arranged therebetween; and a cylindrical lens electrode mounted in the neck portion of the cathode ray tube between said control electrode and said anode electrode surrounding the cathode ray beam, said tubular lens electrode being spaced at one end from said control electrode in direction of said cathode ray beam and having a diameter being greater than the distance from said emitting surface of said cathode to said entrance edge of said anode electrode.

2. In a cathode ray tube having a neck portion, in combination, a plurality of electrodes mounted Within the neck portion and including a cathode having an emitting surface, an anode electrode having an entrance edge for the cathode ray beam, and a control electrode arrangedtherebetwcen; and a cylindrical lens electrode mounted in the neck portion of the cathode ray tube between said control electrode and said anode electrode surrounding the cathode ray beam, said tubular lens electrode being spaced at one end from said control electrode in direction of said cathode ray beam and having a diameter being greater than the distance from said emitting surface of said cathode to said entrance edge of said anode electrode, and said anode having a funnel-shaped portion projecting within one end of said tubular lens electrode.

3. In a cathode ray tube having a neck portion, in combination, a plurality of electrodes mounted within the neck portion and including a cathode having an emitting surface, an anode electrode having an entrance edge for the cathode ray beam, and a control electrode arranged therebetween; and a tubular lens electrode mounted in the neck portion of the cathode ray tube between said control electrode and said anode electrode surrounding the cathode ray beam, said tubular lens electrode being spaced at one end from said control electrode in direction of said cathode ray beam and having a diameter being greater than the distance from said emitting surface of said cathode to said entrance edge of said anode electrode, and being made of a ferro-magnetic material.

4. In a cathode ray tube having a neck portion, in combination, a plurality of electrodes mounted within the neck portion and including a cathode electrode having an emitting surface, an anode electrode having an entrance edge for the cathode ray beam, and a control electrode arranged 'therebetween; and a cylindrical lens electrode mounted in the neck portion of the cathode ray tube and surrounding the cathode ray beam, said lens electrode having one end portion thereof between said control electrode and said anode electrode, said one end portion of said lens electrode having an aperture formed therein permitting the passage of the cathode ray beam therethrough, the other end portion of said lens electrode having a diameter which is smaller than the diameter of said lens electrode and being located adjacent said anode electrode, said lens electrode having a diameter being greater than the distance from said emitting surface of said cathode to said entrance edge of said anode electrode.

5. In a cathode ray tube having a neck portion, in combination, a plurality of electrodes mounted within the neck portion and including a cathode electrode having an emitting surface, an anode electrode having an entrance edge for the cathode ray beam, and a control electrode arranged therebetween; and a cylindrical lens electrode mounted in the neck portion of the cathode ray tube and surrounding the cathode ray beam, said lens electrode having one end portion thereof between said control electrode and said anode electrode, said one end portion of said lens electrode having an aperture formed therein permitting the passage of the cathode ray beam therethrough, said aperture being axially aligned between said emitting surface of said cathode and said anode electrode, the other end portion of said lens electrode having a diameter which is smaller than the diameter of said lens electrode and being located adjacent said anode electrode, said lens electrode having a diameter being greater than the distance from said emitting surface of said cathode to said entrance edge of said anode electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,153,223- Young Apr. 4, 1939 2,173,257 Klemperer Sept. 19, 1939 2,341,764 138 Gier Feb. 15, 1944 2,411,535 Fremlin Nov. 26, 1946 2,490,308 Klemperer Dec. 6, 1949 

